Shelf Sea Biogeochemistry blog

Tuesday, 25 November 2014

More jellies

Ocean research cruise blog of Jonathan Sharples

The children at Churchtown Primary School are I gather busy working
on the questions we asked them about sinking salp poo. The zooplankton
group on board are getting very excited about their results, and already
planning the scientific papers that they want to write. We collected
more of the zooplankton yesterday so that we can make better estimates
of the rate at which they eat and the rate at which they release the
faecal pellets. In an attempt to get an idea of what these delicate
organisms look like in the ocean we attached a few waterproof cameras to
the CTD, and lowered them into the sea surface to record pictures for
half an hour or so. I set the challenge to get a picture of a jellyfish
or salp in the process of releasing faecal pellets into the water. There
was a clear winner (Clare Ostle, from the University of East Anglia),
but she was working very early this morning and is currently in bed – so
I’ll get the photo for tomorrow.

an interesting bucket of jellies

Meanwhile, to help the kids at Churchtown think about this problem,
the picture below has some good examples of the salps (the long, tubular
jellies, connected in spirals) and the tiny jellyfish. Another rally
interesting organism in this photo can also be seen, just about. The
photo looks like it has a fine sprinkling of sawdust in it. These are
tiny colonies of a photosynthesising bacteria called trichodesmium. It’s
special in the ocean because it is a nitrogen fixer – it is able to use
nitrogen gas dissolved in seawater, rather than the form of inorganic
nitrogen (nitrate) that most phytoplankton need. That means they can
grow in areas where nitrate is in very low concentrations, such as the
large areas of open ocean in the sub-tropics. Finding them here is odd,
because there is enough nitrate around and so the trichodesmium should
not have any advantage compared to other phytoplankton. I’ll find out a
bit more about them for another blog entry.